Interpretive Summary: Induced changes in plant quality are important factors mediating indirect interactions between herbivores. Although the sequence of attack has been shown to influence plant responses to herbivores, little is known about how it may affect the outcome of insect-plant-insect interactions. In the current paper, we investigated how induction of a response to the fall armyworm influences resistance of teosinte and cultivated maize to exposure to the western corn rootworm. Fall armyworm infestation had a significant negative effect on western corn rootworm larval establishment in the field and weight gain in the laboratory, but only when fall armyworm arrived on the plant before the root herbivore. When fall armyworm arrived after the root herbivore had established, no negative effects on larval performance were detected. Western corn rootworm beetle emergence was reduced even when the root feeder had established first, indicating that the negative effects were not entirely absent in this treatment. Our results demonstrate that the sequence of arrival can be an important determinant of plant-mediated interactions between insect herbivores in both wild and cultivated plants. Arriving early on a plant may be an important strategy of insects to avoid competition by other herbivores. To fully understand plant-mediated interactions between insect herbivores, sequence-specificity should be taken into account. A thorough understanding of this phenomena could lead to the development of new management tools for insect pests.

Technical Abstract:
Summary
1. Induced changes in plant quality are important factors mediating indirect interactions between herbivores. Although the sequence of attack has been shown to influence plant responses, little is known about how it may affect the outcome of insect-plant-insect interactions.
2. We therefore investigated how induction by the leaf-herbivore Spodoptera frugiperda influences resistance of teosinte (Zea mays mexicana) and cultivated maize (Zea mays mays) against root-feeding larvae of Diabrotica virgifera. Sequence specificity was tested in the field and laboratory for both cultivated maize (Zea mays mays) and its wild relative, teosinte (Zea mays mexicana).
3. S. frugiperda infestation had a significant negative effect on D. virgifera larval establishment in the field and weight gain in the laboratory, but only when S. frugiperda arrived on the plant before the root herbivore. When S. frugiperda arrived after the root herbivore had established, no negative effects on larval performance were detected. Final adult emergence of D. virgifera was reduced even when the root feeder had established first, indicating that the negative effects were not entirely absent in this treatment.
4. The extent of defoliation of the plants was not a decisive factor for the negative effects on root herbivore development, as both minor and major leaf damage resulted in an increase in root resistance and the extent of biomass removal was not correlated with root-herbivore growth. We suggest that leaf-herbivore induced increases in feeding-deterrent and/or toxic secondary metabolites may account for the sequence-specific reduction in root-herbivore performance.
5. Synthesis: Our results demonstrate that the sequence of arrival can be an important determinant of plant-mediated interactions between insect herbivores in both wild and cultivated plants. Arriving early on a plant may be an important strategy of insects to avoid competition by other herbivores. To fully understand plant-mediated interactions between insect herbivores, sequence-specificity should be taken into account.